Troy bilt engine lawnmower.. Runs for a while then it stops.. Won't run after that.. Chainged oil spark plug... Ready to throw it... Had it three years

Sounds fuel related. Dump the gas and open the carb bowl. Clean the carb and check to see if the float adequately dumps fuel when its lowered. Add the prescribed amount of SeaFoam to the new fuel and keep starting it to get the SeaFoam inside the jets.